Filament trimmer head

ABSTRACT

A filament trimmer has an improved trimmer head. The trimmer head includes a spool having crush ribs on its core to prevent contraction of the filament line from warping or otherwise damaging the spool. A slot shaped exit aperture is provided in the head which can be opened up when the head is disassembled to allow the filament line to be more easily placed therein, but which will be closed when the head is fully assembled and will constrain the line against excessive vertical movement. The head includes a line indexing system for feeding out additional line in which one of the groups of the conventional teeth in such system are vertically spaced away from the spool flanges and are placed on a spool core extension. A dirt seal is provided to help prevent from passing around the ground engaging member of the indexing system. Finally, the head includes a self threading drive shaft that forms the attachment threads for the head into the head when the head is threaded onto the drive shaft.

This application is a division of application Ser. No. 08/172,010, filedDec. 22, 1993, pending.

TECHNICAL FIELD

This invention relates to a filament trimmer having a filament line thatis spun about a rotational axis to sever grass, weeds or othervegetation. More particularly, this invention relates to the rotatablehead that stores a supply of filament line on a spool and to theindexing means for periodically rotating the spool relative to the headto feed additional line out from the head.

BACKGROUND OF THE INVENTION

Filament trimmers are well known products that are used to trim grass,weeds, or similar vegetation. They comprise an elongated handle assemblyhaving a hand grip at the upper end and a trimmer head rotatably mountedat the lower end. The trimmer head includes a spool that carries acoiled supply of filament line with a free end of this line extendingradially outwardly from the head. When a motor carried on the trimmer isactivated, the head is rotated to spin the free end of the line aboutthe rotational axis of a drive shaft to allow the free end of the lineto sever grass, weeds and the like.

Despite the relatively well developed nature of these products, thefilament trimmers existing today have various flaws. For example, thespools which carry the coiled supply of the line are typically moldedfrom plastic with the spools having a cylindrical central core on whichthe line is wound. However, the filament line is sensitive toenvironmental conditions, and particularly to the humidity of theambient air, and can expand and contract with changes in theseconditions. When the line contracts on the core, it can in someinstances impose enough of a compressive force on the core to warp ordamage the spool. This can cause the spool to no longer operate properlyor at all, which is a disadvantage.

The filament line carried on the spool typically extends outwardly fromthe spool through an exit aperture in a peripheral sidewall of the head.It can be difficult to thread the line through this aperture duringinstallation of the spool due to the tight spaces found inside the head.Some trimmers have attempted to solve this problem by providing an exitaperture that can be opened up to allow the line to be laid into theaperture when various parts comprising the head are disassembled, but isotherwise closed when the head is in its assembled state. This approachis shown in U.S. Pat. No. 4,672,798 to Ota. However, the exit aperturein this approach is typically formed as an elongated U-shaped slot thatis quite long and which does not constrain the line against verticalmovement as well as the generally circular exit aperture which itreplaces This allows the line to move too much inside the aperture,leading to melting of the line at the aperture due to friction or tobreaking of the line from abrasion.

Most filament trimmer heads have an indexing system for feeding outadditional line to replenish the cutting length whenever the line hasbecome shortened due to wear or breakage. Many of these systems operateby normally locking the spool relative to the head. However, when moreline is required, the spool is unlocked to allow the spool to rotaterelative to the head, thereby feeding out more line from the spool andthus extending the cutting length. In one indexing system of this type,the unlocking of the spool is initiated by bumping the trimmer head, andspecifically a downwardly protruding ground engagement member on thehead, against the ground. Such a ground bump indexing system is shown inU.S. Pat. No. 4,524,515 to Oberg, which is assigned to The Toro Company,the assignee of this application.

Ground bump indexing heads have an opening provided therein to allow theground engagement member to protrude out of the head. This opening,which normally faces the ground, provides an entry point into theinterior of the head for dirt, sand, grit and the like. If the trimmeris operated in dirty environments where a lot of particulate material ispresent, the inside of the trimmer head can become so contaminated thatthe indexing system either no longer works reliably or can be damaged.This requires the trimmer head to be disassembled for cleaning orpotentially requires some of the components of the indexing system to berepaired or replaced.

In addition, most line indexing systems, including ground bump indexingsystems, have various sets of teeth that engage with one another to lockthe spool relative to the head. Some of these teeth are provided on thehead and some on the spool. The most economical way of providing teethon the spool is to mold such teeth integrally into the spool. This ismost often done by molding such teeth into the upper face of one of thespool flanges or into the peripheral edge of one or more of the spoolflanges, as shown in U.S. Pat. No. 4,349,962 to Itagaki et al.

However, if the spool flanges warp even slightly and become distortedfrom their normal horizontal orientation, the teeth carried on the spoolflanges may not reliably engage the teeth provided on the head. Thisleads to imperfect and unreliable operation of the indexing system. Inaddition, outwardly extending teeth on the peripheral edge of the spoolflange unnecessarily increases the diameter of the spool, and thus thediameter of the head, and potentially serve as obstructions that cancatch the line extending out from the spool.

Finally, most filament trimmer heads are mounted onto the motor shaft bybeing threaded onto that shaft. If the threads provided in the head areintegrally molded into the head, the cycle times for molding the headare considerably reduced, leading to a more expensive head. If thethreads are provided in a separate metallic insert, the cost of theinsert, and the cost to mold it in place into the head, must also beborne. Moreover, in an electric trimmer, this threaded metallic inserthas to be molded into a separate plastic part to electrically insulateit. Thus, these two prior art methods of providing attachment threads infilament trimmer heads for securing the head to the motor shaft arerelatively expensive. A less expensive way of attaching the trimmer headto the motor shaft is desirable.

SUMMARY OF THE INVENTION

This invention provides an improved filament trimmer head in whichvarious of the above-noted problems have been solved, to thereby yield atrimmer head of improved reliability and ease of use, while decreasingthe cost to manufacture the head. A filament retention means is carriedinside the head for retaining a supply of filament line with a free endof the line extending radially outwardly from the filament retentionmeans through an exit aperture in the head to form a cutting length ofline located exteriorly of the head. A drive means is provided forrotating the trimmer head about an axis to cause the cutting length ofline to be spun in a cutting plane to sever grass or other vegetation.

One aspect of this invention is to provide means carried on the filamentretention means for absorbing compressive forces caused by contractionof the wound filament line on the core. This means desirably comprises aplurality of crush ribs.

Another aspect of this invention is an improved exit aperture located inthe peripheral sidewall of the head. The exit aperture is selectivelyopenable to allow the line to be placed into the aperture and isselectively closable around the line after the line is placed into theaperture. The aperture in its selectively openable condition comprisesan open-ended slot having a length substantially greater than apredetermined thickness of the line to allow the line to be easilyinserted therein and in its selectively closable condition comprises anaperture that is generally enclosed around the line having a length thatis substantially less than the length of the open-ended slot to helpconstrain movement of the line within the aperture.

Yet another aspect of the invention relates to a trimmer headincorporating indexing means for feeding additional line out from thefilament retention means. In the indexing means contemplated by thisinvention, the trimmer head includes an opening carried in a bottom faceof the trimmer head. An indexing member extends downwardly through theopening to be capable of being engaged against the ground with suchground engagement being effective to actuate the indexing means to feedout additional line. A dirt seal extends radially inwardly from theopening to terminate in a radially innermost edge that is spaced frombut is located adjacent the indexing member, the seal being sized todecrease the size of the gap between the opening and the indexing memberto aid in the prevention of the passage of dirt or other particulatematter through the gap and into the head.

Another aspect of this invention relates to a trimmer head having anindexing means comprising first and second groups of generallyconventional indexing and locking teeth that move relative to oneanother along the axis of rotation during a line indexing operation. Insuch a head, a spool is used to store the line supply. The spool coreincludes a core extension that protrudes to one side past the spoolflanges such that the core extension is located vertically outside ofthe line storage area of the spool. One of the two groups of teeth inthe indexing means is carried on the core extension and is verticallyspaced from the closest spool flange.

A final aspect of this invention relates to an attachment means forattaching the trimmer head to a drive shaft for rotating the same. Thismeans comprises a smooth sided cylindrical bore formed in the trimmerhead during manufacture thereof having a predetermined nominal innerdiameter. A lower end to the drive shaft is suited to be threaded intothe bore. The drive shaft lower end comprises a threaded section thatincludes thread forming screw threads having a predetermined nominalouter diameter sufficiently larger than the inner diameter of the boreto allow the threaded section to form threads in the trimmer headsimultaneously with the shaft being threaded into the bore with suchthreads being sufficient to thereafter hold the trimmer head in place onthe drive shaft during operation of the trimmer.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described more completely hereafter in theDetailed Description, when taken in conjunction with the followingdrawings, in which like reference numerals refer to like elementsthroughout.

FIG. 1 is a side elevational view of a portion of a filament trimmerparticularly illustrating the filament trimmer head of this invention;

FIG. 2 is a cross-sectional view taken along lines 2--2 of FIG. 1,particularly illustrating the top of the filament trimmer head shown inFIG. 1, with a portion thereof broken away to illustrate some of thelocking and indexing teeth in the line indexing system used in the head;

FIG. 3 is a bottom plan view of the filament trimmer head shown in FIG.1;

FIG. 4 is an exploded perspective view of the filament trimmer headshown in FIG. 1;

FIG. 5 is a cross-sectional view of the spool of the filament trimmerhead shown in FIG. 1, taken along lines 5--5 of FIG. 4, particularlyillustrating the crush ribs provided on the spool core for absorbingradially inward compressive forces on the spool core caused bycontraction of the line on the spool core;

FIG. 6 is a cross-sectional view of the filament trimmer head shown inFIG. 1, taken along lines 6--6 in FIG. 1;

FIG. 7 is a partial cross-sectional view of a portion of the filamenttrimmer head shown in FIG. 1, particularly illustrating the attachmentof the head to the motor shaft;

FIG. 8 is an enlarged cross-sectional view of a portion of theperipheral sidewall of the filament trimmer head shown in FIG. 1,particularly illustrating the line exit aperture used in the headsidewall; and

FIG. 9 is an enlarged cross-sectional view of a portion of the filamenttrimmer head shown in FIG. 1, particularly illustrating the dirt sealused at the bottom of the head to help prevent the entry of dirt, sand,and the like into the head.

DETAILED DESCRIPTION

Referring first to FIG. 1, a portion of a filament trimmer of the typewell known in the art, specifically the lower portion of the trimmer, isgenerally illustrated as 2. Trimmer 2 includes a handle assembly 4 thatrotatably mounts a trimmer head 6 at the lower end thereof adjacent theground. Trimmer head 6 houses a means for retaining a supply 9 offilament line 8 such that a cutting length of line, identified as 10,extends radially outwardly from head 6 when head 6 is rotated byoperation of a motor or engine (not shown) carried on trimmer 2. Whensuch rotation occurs, cutting length 10 is made rigid by centrifugalforce and is effective to sever grass, weeds, and the like at whateverheight is determined by how closely the user positions head 6 adjacentthe ground. Trimmer 2 includes a protective shield 11 between the userand cutting length 10 of line 8.

The means for retaining the filament line supply 9 comprises a storagespool 12 contained inside head 6. This invention relates to variousimprovements to head 6 and spool 12 that solve the various problemsexisting in prior art devices as discussed in the Background of theInvention section of this application. One of these improvements relatesto how trimmer head 6 is attached to the drive shaft used to rotate head6. Other than for a specific type and shape to the lower end of thisdrive shaft, trimmer head 6 can be used on any filament trimmer,including any electric trimmer or any gasoline engine powered trimmer.Consequently, the structure of trimmer 2, except for the type and shapeof the lower end of the drive shaft, is not important to this inventionand is not specifically illustrated in the drawings.

The Trimmer Head

The Two-Part Construction

Trimmer head 6 is made in two parts that are separably joined togetherto form a complete trimmer head. These parts may be quickly detachedfrom one another and quickly reconnected to one another to allow theuser to easily remove and replace spool 12 inside trimmer head 6. Thisneeds to be done to repair or replace a damaged spool 12, to wind moreline on a spool 12 that has exhausted its prior line supply 9, toreplace the entire spool 12 with a new spool 12 having a fresh supply 9of line, to straighten out tangled line, etc. It is obviously desirableto provide the user with easy access to spool 12 inside trimmer head 6so that these and similar tasks are easy to accomplish.

The two separable parts that comprise trimmer head 6 are a housing 14and a separable cap 16. Referring to FIGS. 1, 4 and 6, housing 14 has aninverted, cup-shaped configuration that includes a closed upper end anda cylindrically shaped peripheral sidewall 18 that is at least a fewinches deep and which terminates in an exterior lower edge 20. Cap 16comprises a circular, generally flat, plate-like member that isseparably attached to housing 14 and when so attached abuts againstlower edge 20 of cylindrical sidewall 18. Cap 16 includes a circularopening 22 in the center thereof to allow a portion of spool 12 toprotrude out of trimmer head 6 to allow this portion of spool 12 to bebumped or tapped on the ground to feed more line from spool 12. Thisline indexing operation, and the structure inside head 6 and on spool 12for allowing this to occur, will be described in more detail hereafter.

When connected together, housing 14 and cap 16 form a substantiallyenclosed chamber or cavity 24 in which spool 12 is carried. Many ways ofseparably attaching cap 16 and housing 14 together could be used.However, one preferred method is to form cap 16 with a plurality ofvertically extending flexible tangs 26 that are circumferentially spacedaround the periphery of cap 16. Each tang 26 includes an outwardlyextending hook 28 at its upper end having a downwardly facing hooksurface 30. Sidewall 18 of housing 14 includes a plurality of verticalpassages 32 that are equal in number to the number of tangs 26 and whichare positioned around sidewall 18 to correspond to the spacing of tangs26. Tangs 26 are formed such that the hooks 28 have a natural, radiallyoutward bias to allow hooks 28 to snap into small windows (not shown)provided in sidewall 18 at the upper ends of passages 32.

Accordingly, housing 14 and cap 16 have a releasable snap fit connectionwith one another. To release cap 16 from housing 14, the user only hasto press inwardly with his or her fingers through the windows on thesidewall 18 of housing 14 until the hooks 28 on tangs 26 are pressedradially inwardly a sufficient distance to disengage the hook surfaces30 from the lower edge of the windows. The force of a spring 80, alongwith a downward pull on cap 16 if necessary, will move cap 16 downwardlyto remove cap 16 from housing 14, thus opening up cavity 24 in whichspool 12 is carried. Conversely, to reattach cap 16 to housing 14, theuser need only circumferentially align tangs 26 with the location of thevertical passages 32 and push upwardly on cap 16 until the hooks 28 onthe upper ends of tangs 26 reach the sidewall windows and snap radiallyoutwardly.

The Exit Aperture

One novel feature of trimmer head 6 is the structure used to form anexit aperture 34 in sidewall 18 of housing 14. Aperture 34 allows thefilament line 8 on spool 12 to be easily threaded through aperture 34when cap 16 is removed from housing 14. However, during operation oftrimmer 2, aperture 34 otherwise relatively closely constrains the line8 against any substantial vertical up and down movement to preventfriction and abrasion of line 8 against aperture 34 and thereby helpprevent line 8 from melting or breaking at the aperture. This isaccomplished without any steps required by the user other than forhaving to remove and then reattach cap 16 to housing 14.

Exit aperture 34 comprises a vertical, U-shaped slot 36 in sidewall 18of housing 14. Slot 36 has the closed end 38 of the U located in theinterior of sidewall 18 with slot 36 extending downwardly from theresuch that the open end 40 of the U is located at lower edge 20 ofsidewall 18. See FIG. 4. Thus, when cap 16 is not connected to housing14, slot 36 is effectively open at the bottom thereof, i.e. at the openend 40 of the U, to allow the user to place the filament line 8 intoslot 36 without having to try and thread line 8 through an enclosedcircular aperture located in the middle of sidewall 18. However, exitaperture 34 is completed and becomes substantially enclosed to surroundline 8 and prevent line 8 from falling out of slot 36 when cap 16 isreattached to housing 14. Cap 16 will then extend over and close off theopen end 40 of slot 36 to thereby form an enclosed exit aperture 34.

Referring again to FIG. 6, it is preferred that line 8 exit from a pointin the interior of sidewall 18, and preferably from about the midpointof sidewall 18, because this will center exit aperture 34 over the depthof the line storage area on spool 12. In other words, as line 8 pays outfrom the top to the bottom of its supply 9, the maximum angle formedbetween line 8 and exit aperture 34 is about the same whether line 8 ispaying out of the top rung of the coiled supply 9 or the bottom rung ofsupply 9. This is a reason for extending the top of slot 36, i.e. theclosed end 38 of the U, up into the interior of sidewall 18 toapproximately the midpoint of sidewall 18.

However, in doing so, the otherwise open length of slot 36 issubstantially longer than the diameter of line 8, on the order of 7 to 9times longer than the line diameter. This extended slot length providestoo much room for line 8 to vibrate up and down in slot 36 duringoperation of trimmer 2. This vibration and vertical movement can lead tounnecessarily short line life due to undesirable friction and melting ofline 8 at aperture 34 or due to abrasion of line 8 with breakage of line8 at aperture 34.

Trimmer head 6 of this invention avoids this result by shortening thelength of slot 36, or by filling in approximately half the length ofslot 36, to form, in effect, an aperture 34 having a length onlyslightly greater than the diameter of line 8, preferably from about 3 to4 times the diameter of line 8. This is most easily done by forming anupwardly extending tab 42 on cap 16 which tab 42 is located to bereceived inside slot 36 when cap 16 is snapped onto housing 14. Theheight of tab 42 is chosen so that the upper face 44 of tab 42 is spacedbeneath closed end 38 of the U-shaped slot 36 by the required amount. Ina trimmer with line 8 having a diameter of 0.065 inches, slot 6 whenunobstructed by tab 42 has a length of approximately 0.500 inches andwhen obstructed by tab 42 has a length of approximately 0.250 inches.

Tab 42 is effective to prevent excessive vertical vibration and movementof line 8 in slot 36 and thereby extends the life of line 8. Anotherdesirable result achieved from using tab 42 is that line 8 is preventedfrom wedging in any gap at the bottom of slot 36 that might be presentbetween cap 16 and lower edge 20 of housing sidewall 18. Tab 42 simplykeeps line 8 spaced up above the junction between cap 16 and sidewall18. This invention provides an exit aperture 34 that can be opened up,by removing cap 16, to allow line 8 to be easily slipped into aperture34, but which can thereafter be closed to form an enclosed aperturearound line 8 which prevents excessive vertical line movement simply bysnapping cap 16 into place on housing 14.

Referring now to FIG. 8, the vertical sides 46 of exit aperture 34preferably have a curved configuration to provide curved bearingsurfaces for line 8 as it extends out through exit aperture 34.Preferably, exit aperture 34 is formed by integrally molding intosidewall 18 a slot 36 of the appropriate configuration and by then pressfitting into that slot 36 a U-shaped metal insert 47 that providesmetallic bearing surfaces for the filament line. However, exit aperture34 could simply comprise a slot 36 molded into sidewall 18 of trimmerhead 6 without using metallic insert 47 in slot 36. Trimmer head 6 ispreferably molded from any suitably hard plastic material.

Referring again to FIG. 8, the side surfaces 45 of the line constrainingtab 42 received inside slot 36 preferably should be shaped to correspondto and match the shape of sides 46 of slot 36. Thus, when an exitaperture 34 having curved sides 46 is used, as is the case here, sidesurfaces 45 of tab 42 should also be similarly curved to closely lieadjacent to sides 46 of slot 36. This minimizes any vertical gaps thatmight occur between side surfaces 45 of tab 42 and vertical sides 46 ofslot 36 to prevent line 8 from being extruded into or getting pinched inthese gaps. Thus, in addition to having the required height needed tofill in the length of slot 36, tab 42 should be sized to be closelyreceived across the width of slot 36 with the side surfaces of tab 42having matching configurations to the vertical sides 46 of slot 36.

Desirably, cap 16 includes two tabs 42, spaced circumferentially apartby 180°, to ease the task of aligning tab 42 with slot 36, and toprovide some balance to cap 16. In this regard, the tab 42 on the otherside of cap 16 is received in a vertically extending, enclosed pocket 48that is formed in sidewall 18 of housing 14. Tabs 42 are identical,however, so that either tab 42 may be received in the aperture formingU-shaped slot 36. Thus, cap 16 can be snapped up onto the lower end ofhousing 14 in two different positions with one tab 42 being received inslot 36 and the other tab 42 being received in enclosed pocket 48. SeeFIG. 6.

The Drive Shaft Attachment

Trimmer head 6 has to be secured to a downwardly extending drive shaft50 that is used to rotate trimmer head 6. In an electrically poweredtrimmer 2, an electric drive motor is often mounted on the lower end oftrimmer 2 in a housing immediately above trimmer head 6. In this case,drive shaft 50 comprises the vertically extending motor shaft of theelectric motor. In a gasoline engine powered trimmer, the gasolineengine is often mounted at the top end of the trimmer and a long drivecoupling member, or series of drive coupling members, extends down fromthe engine to connect to the trimmer head 6. Thus, the phrase "driveshaft" as used herein is simply meant to refer to that shaft-likeelement that attaches to trimmer head 6, whether that be the motor shaftof an electrically powered trimmer or the lowermost drive couplingmember in a gasoline powered trimmer.

In known filament trimmers, the drive connection is often made byproviding a threaded bore in the top of the trimmer head which screwsonto a threaded drive shaft. In some cases, the threaded bore isprovided by threads that are integrally molded into the trimmer head. Inother cases, a separate threaded insert, often made of metal, isprovided. This insert, which is usually a separate part, has to beelectrically insulated. This is done by first molding the insert into aseparate plastic part in a separate molding operation. The plastic partcarrying the insert is then fixed into the trimmer head to receive thethreaded drive shaft. However, the need to provide these threaded boresin the trimmer head increases the cost of the trimmer head.

Trimmer head 6 of this invention utilizes an improved, less expensive,way of connecting trimmer head 6 to drive shaft 50. It comprises anelongated, downwardly extending hub 52 in the center of the top end ofhousing 14. Hub 52 is molded to have a smooth, vertically extending,cylindrical bore 54 that is integrally molded into hub 52 when housing14 is molded. Bore 54 is provided with an inner diameter of apredetermined value, e.g. a nominal inner diameter of 0.270 inches,which is indicated in FIG. 6 as d₁.

Referring now to FIG. 7, the lower end of drive shaft 50 includes athreaded section 56 made of thread forming screw threads, e.g. such asthose known by the tradename of plastite. The outer diameter of threadedsection 56 is significantly greater than, e.g. approximately twenty toforty thousandths of an inch greater than, inner diameter d₁ of bore 54.Thus, when threaded section 56 is threaded down into smooth bore 54, theoversized thread forming screw threads on section 56 will deform theplastic material comprising hub 52 to form the screw threads needed toreceive threaded section 56. This is done at the same time as trimmerhead is being affixed to drive shaft 50.

It is preferred that the very bottom of drive shaft 50 be formed with acylindrical pilot portion 58 having an outer diameter that isapproximately the same as, e.g. a nominal outer diameter that is thesame or is a few thousandths of an inch greater or less than, innerdiameter d₁ of bore 54. In addition, it is also preferred that threadedsection 56 be made with a two lead thread. Using a two lead thread helpsto insure that the threaded section 56 is properly aligned on lower endof drive shaft 50 when the threads comprising section 56 are rolled ontothe lower end of drive shaft 50 during manufacture thereof. The pilotportion 58 will travel down bore 54 in advance of threaded section 56.The purpose of using both of these elements, namely both pilot portion58 and the two lead thread on threaded section 56, is to properly alignhousing 14 on drive shaft 50 when housing 14 is being threaded ontodrive shaft 50.

By providing only a smooth bore 54 in hub 52 of housing 14 duringmanufacture of housing 14, the cycle times for molding housing 14 can begreatly increased as there is no need to spin housing 14 off a screwforming mandrel before pulling it out of the mold. Instead, smooth bore54 is simply molded in hub 52 when housing 14 is molded. This can bedone without decreasing the mold cycle times otherwise needed to moldhousing 14, and reduced tool costs and maintenance should also result.Thus, bore 54 can be molded into housing 14 with very little, if any,increase in cost. Moreover, there is obviously no need to provide aseparate threaded insert for use in the housing and to mold this insertinto the housing or into a separate molded part.

The attachment of trimmer head 6 to drive shaft 50 is made, and thesimultaneous formation of the necessary screw threads in hub 52 occurs,when trimmer head 6 is threaded onto drive shaft 50. This is done duringmanufacture of trimmer 2 with pilot portion 58 being first received inbore 54 and with threaded portion 56 serving to bite into and rigidlyaffix drive shaft 50 to housing 14 due to the oversized nature of thethreads relative to bore 54. A groove 51, or some other visual mark orindicia, can be placed on the exterior of the lower end of drive shaft50 as an aid in the manufacture of trimmer head 6. Drive shaft 50 isfully inserted into hub 52 when groove 51 becomes centered on the topsurface of hub 52 (as shown in FIG. 7) which signals to the assemblerthat head 6 is completely threaded onto drive shaft 50 and the threadingof head 6 onto drive shaft 50 should be stopped. Pilot portion 58 andthe use of a two lead thread help provide the necessary alignment andguidance to ensure that housing 14 threads onto drive shaft 50 straightand is not canted at an angle during the threading operation.Accordingly, trimmer head 6 of this invention is less expensive tomanufacture and assemble because there is no need to provide threads inbore 54 prior to the time head 6 is threaded onto drive shaft 50.

Trimmer head 6 is built such that drive shaft 50 is not speciallyprotected or enclosed inside a motor bracket or inside recessed portionsof housing 14 as drive shaft 50 extends between the lower portion oftrimmer 2 and head 6. Instead, drive shaft 50 comprises an exposed metalshaft that simply extends down into trimmer head 6 from the lowerportion of trimmer 2. When trimmer 2 is an electrically powered trimmer,drive shaft 50 normally comprises the motor shaft of the electric motorwhich rotates head 6. This electric motor is normally housed in thelower portion of trimmer 2 immediately above head 6.

When trimmer 2 is an electrically powered trimmer, a first set of radialcooling fins 55 are normally provided on top of head 6 for generating anair flow that cools the electric drive motor. In addition, trimmer head6 of this invention comprises a second set of radial fins 57 that areshorter than first fins 55 with the second fins 57 being interposedbetween adjacent ones of the first fins 55. Together, fins 55 and 57 aresufficiently close together to prevent the fingers of the user, whichare simulated by a quarter inch probe in a known test that is performedon these types of products, from being inserted into the gap between thetop of head 6 and the bottom of the lower portion of trimmer 2 andtouching the exposed motor shaft 50 of such an electric trimmer. Thus,the safety of head 6 is enhanced simply by appropriately spacing fins 55and 57 on the top of trimmer head 6.

The Dirt Seal

Referring now to FIG. 9, trimmer head 6 further includes means forpreventing dirt, sand and similar debris from entering into trimmer head6 through opening 22 in cap 16. This means includes a triangularlyshaped, knife edged dirt seal 60 which extends radially inwardly fromthe inner diameter of opening 22 towards a cylindrical portion 62 of anouter peripheral wall of a ground bump button 64 on spool 12. Dirt seal60 is preferably integrally molded into cap 16 in the form of an annularflange which comes to a sharp point at its radially innermost edge (i.e.about 0.010 inches thick at its radially innermost edge which is aboutas sharp as it can be molded). Dirt seal 60 is also preferablypositioned adjacent the bottom face of cap 16 at the lowermost edge ofopening 22.

The purpose of dirt seal 60 is to cut down the normal gap or distancebetween opening 22 and cylindrical wall portion 62 of ground bump button64 by at least 50%, and preferably by at least 75%, such that theremaining gap is only a few thousandths of an inch wide. This preventsthe easy entry of dirt, sand or similar debris into trimmer head 6through opening 22 and helps to prevent the wedging of sand or dirtparticles between cap 16 and spool 12. In addition, seal 60 has a wipingaction relative to ground bump button 64 that will tend to wipe away anydebris particles as ground bump button 64 moves up and down relativelyto trimmer head 6 during a line indexing operation.

Dirt seal 60 is preferably integrally molded as part of cap 16 for easeof manufacture and for cost reasons, and thus will be made from theusual plastic materials typically used in filament trimmer heads.Because seal 60 is rigid and approaches to within a few thousandths ofcylindrical wall portion 62, it is preferred that some means be used tohelp center ground bump button 64 within opening 22 to keep ground bumpbutton 64 from periodically wobbling into engagement with or otherwisecontacting dirt seal 60 during operation of trimmer 2. Engagementbetween ground bump button 64 and seal 60 would potentially chip or wearaway dirt seal 60 lessening its usefulness, or might score or damageground bump button 64.

The centering means comprises an annular, upwardly facing chamferedshoulder 66 provided on an annular shell 67 in the interior of cap 16surrounding opening 22. A plurality of chamfered, triangular ribs 68 areprovided on the upper portion of cylindrical wall portion 62 of groundbump button 64. See FIG. 4 as well as FIG. 9. Ribs 68 have an angle thatmatches the angle of chamfered shoulder 66. Ribs 68 will engage againstchamfered shoulder 66 when ground bump button 64 is in its lowermostposition during normal operation of trimmer 2 to help keep button 64properly centered within dirt seal 60. In this regard, ribs 68 arepreferred over a downwardly facing, annular surface on spool 12 becausesuch ribs 68 will better prevent any sand or dirt particles that mightget past dirt seal 60 form binding between spool 12 and chamferedshoulder 66.

The centering effect of shoulder 66 and ribs 68 is lost when ground bumpbutton 64 is raised during a line indexing operation. However, the outerperipheral wall of button 64 has an inwardly tapered, conical lower end69 which tends to slightly increase the gap between seal 60 and button64 when button 64 is in contact with the ground and is raised relativeto cap 16. Thus, less centering is needed in this raised condition ofbutton 64, and button 64 is raised in a line indexing operation onlyrarely during normal operation of trimmer 2.

The Spool

Spool 12 comprises means for carrying or retaining the supply 9 offilament line 8. Spool 12 includes a cylindrical core 70 on which line 8is wound to form a coiled supply 9 having multiple turns on core 70. Theouter or free end of line 8 extends radially outwardly from core 70through exit aperture 34 to form the cutting length 10 of line 8. Whilecore 70 preferably is cylindrically shaped and is formed by animperforate solid wall, any core defining shape or structure whichallows line 8 to be wound thereon could be used.

Spool 12 includes top and bottom spool flanges 72 and 74 between whichthe turns of the stored filament line 8 are received. Spool flanges 72and 74 are circular and are approximately the same size, each beingslightly smaller than the inside diameter of spool receiving cavity 24provided inside trimmer head 6. Ground bump button 64 extends integrallydownwardly from bottom spool flange 74 to extend out through opening 22in trimmer head 6 past dirt seal 60. Top spool flange 72 includes aradial slot 76 which receives and holds the radial outer end of line 8to prevent the uncoiling of line 8 from spool 12 prior to the time line8 is threaded through aperture 34. Spool 12 is integrally molded as asingle unit from a suitably hard and durable plastic material.

Spool 12 of this invention includes means for absorbing any radiallyinward forces that might be imposed by filament line 8 on core 70 ofspool 12. Nylon filament line of the type commonly used in filamenttrimmers is susceptible to environmental conditions, particularly to thehumidity in the air as such line is somewhat hygroscopic, and can expandor contract with changes in these conditions. If line 8 contractsbecause of such conditions, it can sometimes squeeze inwardly on core 70with sufficient force that it deforms spool 12 causing spool flanges 72and 74 to warp out of their normal horizontal orientations orpotentially can even damage spool core 70 due to high stress. Thisinvention provides means for absorbing this compressive force to avoidthese consequences.

The force absorbing means utilized in this invention comprises aplurality of crush ribs 78 that are integrally molded onto spool core 70between the upper and lower flanges 72 and 74 of spool 12. Crush ribs 78extend vertically and are spaced circumferentially around spool core 70.Referring to FIG. 5, ribs 78 are quite thin in relation to the thicknessof spool core 70 and are deformable under the types of compressionforces that might be caused by the contraction of line 8 on spool core70. The deformation of these crush ribs 78 prevents these forces fromwarping or damaging spool 12, thus contributing to the life of spool 12and to the continued proper operation of trimmer head 6.

The Line Indexing Means

Trimmer head 6 includes means for allowing the filament line to beperiodically indexed or fed out of trimmer head 6 to replenish andextend the cutting length 10 of line 8 outside of trimmer head 6. Thismust periodically be done during operation of trimmer 2 because line 8will sometimes break or gradually wear away due to contact with theground, with trees, or the like.

The indexing means of this invention is of the well known ground bumptype. It includes a spool 12 that is movable vertically inside trimmerhead 6 between a lowered position, shown in solid lines in FIG. 6, and araised position, shown in phantom lines in FIG. 6. A spring 80 is usedinside head 6 to normally bias spool 12 to its lowered position.However, if the filament trimmer 2 is tapped on the ground by the user,the engagement of ground bump button 64 with the ground will move spool12 upwardly relative to trimmer head 6 to its raised position. When head6 is lifted up off the ground, spring 80 is effective to move it backdown to its lowered position.

Trimmer head 6 and spool 12 are provided with two groups of teeth thatrotationally lock spool 12 and trimmer head 6 relative to one another inboth the lowered and the raised positions of spool 12. Either trimmerhead 6 or spool 12 can integrally carry the first group of teeth. Thisgroup comprises two sets 82 and 84 of circumferentially spaced indexingteeth with the teeth 82a, 82b, 82c, etc. in the first set 82 beingrotationally offset relative to the teeth 84a, 84b, etc. in the secondset 84. See FIG. 2. The teeth in the first set 82 are also verticallyoffset relative to the teeth in the second set 84. See FIG. 6.

Whichever one of trimmer head 6 or spool 12 does not carry the firstgroup of teeth, namely the first and second sets 82 and 84 of indexingteeth, will carry the second group of teeth used in the indexing means.This second group of teeth comprises at least one set 86 ofcircumferentially spaced locking teeth 86a, 86b, 86c, etc. See FIGS. 2,5 and 6. The locking teeth set 86 engage against the first set 82 ofindexing teeth in the lowered position of spool 12 to rotationally fixspool 12 and trimmer head 6 against rotation relative to one another. Inaddition, the locking teeth set 86 also engage against the second set 84of indexing teeth in the raised position of spool 12 to againrotationally fix spool 12 and trimmer head 6 against rotation relativeto one another.

In trimmer 2 of this invention, the second group of teeth in theindexing means, namely the set 86 of locking teeth, are integrallymolded on spool 12 and the first group of teeth in the indexing means,namely the vertically and rotationally staggered sets 82 and 84 ofindexing teeth, are integrally molded in housing 14 of trimmer head 6.However, this could be reversed if so desired. The single set 86 oflocking teeth in the first group could be integrally molded into housing14 of trimmer head and the two sets 82 and 84 of indexing teeth in thesecond group could be integrally molded as part of spool.

A novel feature of this invention is that the teeth in whatever group iscarried by spool 12 are not molded as part of either spool flange 72 or74, but are molded into an extension 90 of spool core 70 to bevertically spaced from spool flanges 72 or 74. Thus, as shown in FIG. 6,the locking teeth 86a, 86b, 86c in the second group of teeth are locatedabove top spool flange 72 for engagement with the sets 82 and 84 ofindexing teeth that are similarly located above top spool flange 72. Theteeth 86 carried on spool 12 preferably simply extend radially outwardlyfrom spool core extension 90 as shown in the drawings. Alternatively,these teeth could be formed around the periphery of a short, horizontal,annular flange that protrudes radially outwardly from spool coreextension 90.

Whichever is the case, the array of teeth carried on spool 12 preferablyhas an outer diameter, indicated as d₂ in FIG. 5, that is significantlyless than the diameter of spool flanges 72 or 74. The teeth carried byhousing 14, namely the indexing teeth sets 82 and 84, are alsopreferably located radially inwardly of the periphery of spool flanges72 or 74. See FIG. 6. This allows the diameter of spool 12 to be kept toa minimum since none of the teeth comprising the indexing means extendradially outwardly past the outer peripheral edges of spool flanges 72or 74. It also prevents any possibility that line 8 extending outwardlyfrom spool 12 will catch or tangle on any of the teeth in the indexingmeans.

Forming at least one of the groups of teeth required for the indexingmeans directly on spool 12 decreases the cost of trimmer head 6 since aseparate tooth carrying element is no longer required. Not using spoolflanges 72 or 74 to carry the teeth provided on spool 12 and placingsuch teeth vertically away from spool flanges 72 or 74 allows theseteeth to remain in a proper horizontal orientation even if the adjacentspool flange warps or bends to some degree. Keeping the outer diameterd₂ of these teeth to a value which is only slightly greater than spoolcore 70 and is significantly less than the diameter of spool flanges 72or 74 enhances the strength of these teeth and decreases any possibilitythat they themselves might warp or bend. Thus, the indexing system ofthis invention is less expensive to manufacture than prior known systemsin which these teeth are placed on a separate element, and are morereliable in operation than prior known systems in which these teeth arecarried on the spool flanges.

The indexing means of this invention works in the manner that is wellknown for ground bump systems. It basically allows spool 12 and trimmerhead 6 to rotate relative to one another during those times when spool12 and trimmer head 6 are unlocked, i.e. when spool 12 is moving betweenits lowered position and its raised position and vice versa. Forexample, a first increment of line is fed out when ground bump button 64is bumped on the ground to raise spool 12 and the locking teeth in set86 disengage the indexing teeth in the first set 82. Spool 12 is thenunlocked relative to head 6 so that centrifugal force acting on line 8is effective to rotate spool 12 during the time before the locking teethin set 86 reengage against the indexing teeth in the second set 84. Theincrement of the line that is extended is equal to the amount of theangular offset between the indexing teeth in the two sets 82 and 84.

Similarly, a second increment of line is fed out during downward spoolmovement when ground bump button 64 is lifted off the ground and thelocking teeth set 86 disengages the indexing teeth in the second set 84and reengages against the indexing teeth in the first set 82.

Many of the features of trimmer head 6 as disclosed herein can be usedindependently of one another. For example, the force absorbing meanscomprising crush ribs 78 can be used on any spool that stores filamentline that is subject to contraction, whether or not such spool is usedin conjunction with a ground bump indexing system or even with anyindexing system that feeds line out while the trimmer is operating.Similarly, the novel exit aperture 34 can be used in filament trimmershaving conventional line storage spools and regardless of whether anyline indexing system is used. Accordingly, the scope of this inventionis to be limited only by the appended claims.

We claim:
 1. An improved filament trimmer of the type having a trimmerhead, a spool having a spool core and upper and lower spool flangesextending radially outwardly from the core to define a line storage areabetween the spool flanges with the spool flanges having outermostperipheral edges, a supply of filament line wound around the core andlocated in the line storage area of the spool with a free end of theline extending radially outwardly from the spool to form a cuttinglength of line located exteriorly of the head, drive means for rotatingthe trimmer head about an axis to cause the cutting length of line to bespun in a cutting plane to sever vegetation, and indexing means forfeeding additional line out from the spool, wherein the indexing meansincludes a first group of indexing teeth comprising first and secondsets of indexing teeth that are spaced apart relative to one anotheralong the axis of rotation, the indexing teeth in each set thereof beingcircumferentially spaced apart relative to one another and the indexingteeth in the first and second sets thereof being circumferentiallyoffset relative to one another, the indexing means further including asecond group of locking teeth comprising at least one set of lockingteeth in which the locking teeth are circumferentially spaced apartrelative to one another, the locking teeth in the second group beingalternately engageable with the indexing teeth in the first and secondsets of indexing teeth in the first group in response to relativereciprocal motion along the axis of rotation between the first andsecond groups of teeth, wherein the improvement relates to the indexingmeans and comprises:(a) the spool including a core extension attached tothe spool core and which vertically protrudes past the spool flangessuch that the core extension is located vertically outside of the linestorage area of the spool; (b) wherein one of the two groups of teeth inthe indexing means is carried by and integrally formed on the coreextension and is vertically spaced from the spool flange closest to theone group of teeth carried by the core extension, wherein the teeth inthe one group of teeth carried by the core extension extend radiallyoutwardly from the core extension but do not extend radially outwardlypast the outermost peripheral edges of the spool flanges; and (c)wherein the spool including the spool core, the spool flanges, the coreextension and the one group of teeth carried by the core extension areintegrally molded in one piece from a plastic material.
 2. An improvedfilament trimmer as recited in claim 1, wherein the spool core has apredetermined outside diameter, and wherein the core extension has anoutside diameter that is generally the same as the outside diameter ofthe spool core.
 3. An improved filament trimmer as recited in claim 1,wherein the spool core is hollow having a predetermined wall thickness,and wherein the core extension is hollow having a wall thickness whichis generally the same as the wall thickness of the spool core.
 4. Animproved filament trimmer as recited in claim 1, wherein the teeth inthe one group of teeth carried by the core extension are substantiallyparallel to the spool flanges.
 5. An improved filament trimmer asrecited in claim 1, wherein the other group of teeth are carried in thetrimmer head, extend radially inwardly relative to the spool core, andare positioned radially inwardly from the outermost peripheral edges ofthe spool flanges to minimize the size of the spool.
 6. An improvedfilament trimmer of the type having a trimmer head, a spool having aspool core and upper and lower spool flanges extending outwardly fromthe core to define a line storage area between the spool flanges, asupply of filament line wound around the core and located in the linestorage area of the spool with a free end of the line extending radiallyoutwardly from the spool to form a cutting length of line locatedexteriorly of the head, drive means for rotating the trimmer head aboutan axis to cause the cutting length of line to be spun in a cuttingplane to sever vegetation, and indexing means for feeding additionalline out from the spool, wherein the indexing means includes a firstgroup of indexing teeth comprising first and second sets of indexingteeth that are spaced apart relative to one another along the axis ofrotation, the indexing teeth in each set thereof being circumferentiallyspaced apart relative to one another and the indexing teeth in the firstand second sets thereof being circumferentially offset relative to oneanother, the indexing means further including a second group of lockingteeth comprising at least one set of locking teeth in which the lockingteeth are circumferentially spaced apart relative to one another, thelocking teeth in the second group being alternately engageable with theindexing teeth in the first and second sets of indexing teeth in thefirst group in response to relative reciprocal motion along the axis ofrotation between the first and second groups of teeth, wherein theimprovement relates to the indexing means and comprises:(a) the spoolhaving a tubular member having upper and lower ends, wherein the spoolflanges are located on the tubular member between the upper and lowerends thereof such that a middle portion of the tubular member is locatedbetween the spool flanges to form the spool core, an upper portion ofthe tubular member extends above the upper spool flange to form anextension of the spool core, and a lower portion of the tubular memberextends below the lower spool flange; (b) wherein one of the two groupsof teeth in the indexing means is carried on the core extension formedby the upper portion of the tubular member to be vertically spaced abovethe upper spool flange, wherein the teeth in the one group of teethcarried by the core extension are substantially parallel to the upperspool flange and are located radially inwardly from an outermostperipheral edge of the upper spool flange; and (c) wherein the lowerportion of the tubular member has a closed lower end forming a groundbump member that is bumped against the ground to initiate line indexing.7. An improved filament trimmer as recited in claim 6, wherein the teethin the one group of teeth carried by the core extension overlie theupper spool flange.
 8. An improved filament trimmer of the type having atrimmer head, a spool having a spool core and upper and lower spoolflanges extending radially outwardly from the core to define a linestorage area between the spool flanges with the spool flanges havingoutermost peripheral edges, a supply of filament line wound around thecore and located in the line storage area of the spool with a free endof the line extending radially outwardly from the spool to form acutting length of line located exteriorly of the head, drive means forrotating the trimmer head about an axis to cause the cutting length ofline to be spun in a cutting plane to sever vegetation, and indexingmeans for feeding additional line out from the spool, wherein theindexing means includes a first group of indexing teeth comprising firstand second sets of indexing teeth that are spaced apart relative to oneanother along the axis of rotation, the indexing teeth in each setthereof being circumferentially spaced apart relative to one another andthe indexing teeth in the first and second sets thereof beingcircumferentially offset relative to one another, the indexing meansfurther including a second group of locking teeth comprising at leastone set of locking teeth in which the locking teeth arecircumferentially spaced apart relative to one another, the lockingteeth in the second group being alternately engageable with the indexingteeth in the first and second sets of indexing teeth in the first groupin response to relative reciprocal motion along the axis of rotationbetween the first and second groups of teeth, wherein the improvementrelates to the indexing means and comprises:(a) the spool including acore extension attached to the spool core and which vertically protrudespast the spool flanges such that the core extension is locatedvertically outside of the line storage area of the spool, wherein thespool core has a predetermined outside diameter, and wherein the coreextension has an outside diameter that is generally the same as thespool core; and (b) wherein one of the two groups of teeth in theindexing means is carried by and integrally formed on the core extensionand is vertically spaced from the spool flange closest to the one groupof teeth carried by the core extension, wherein the teeth in the onegroup of teeth carried by the core extension extend radially outwardlyfrom the core extension but do not extend radially outwardly past theoutermost peripheral edges of the spool flanges.